This invention is directed to an energy absorbing device and, more particularly, to one in which energy is absorbed under tensile stress and deflection.
Energy absorbing devices of various types have been used to cushion impact upon collision, especially in bumper systems for automotive vehicles. Until recently bumper systems on automotive vehicles were merely an external body component used to finish off the appearance of a vehicle. However, as a result of public demand and legislative action a more sophisticated design for bumpers is now obligatory. Much emphasis is placed on the protection of vehicles against high repair costs due to collision damage and, thus, various types of energy absorbing bumper systems have been suggested. Hydraulic shock-absorber type systems have been used most extensively. These systems operate by forcing fluid through small apertures, and use air pressure or metallic springs to provide for return of the device to its normal operating position for repeated impacts. Other energy absorbing systems employ plastic or rubber blocks, both solid and hollow, and cushion the shock by compression. Such energy absorbing devices have not been entirely satisfactory. For example, hydraulic devices are generally quite heavy and must contain a liquid. The weight of the device is an important consideration, especially today when interest in the automotive industry is making lighter weight vehicles. Systems that use plastic or rubber blocks suffer from disadvantages in restorability. Mechanical energy absorbing systems composed of metal springs are not fully satisfactory because they have a high coefficient of restitution and thus can constitute a danger due to loss of vehicle control as the vehicle is fired back from the object it has hit. Energy absorbing devices should not only be relatively light but they must be strong enough to withstand rather severe low speed impact. For example, in the impact of a 3000 pound automobile hitting a fixed object at 5 miles/hour about 30,000 inch-pounds of energy must be absorbed by the energy-absorbing device over displacement through a short distance, e.g., about two inches. Further, an energy absorbing device used in a bumper system for automotive vehicles must be vibration free, permit the vehicle to be jacked by the bumper, and should be self-restoring after low speed impact. The present invention provides such a vibration-free energy absorbing mechanism that is relatively light weight, can withstand repeated impact, is self-restoring, permits jacking of the vehicle by the bumper, is reliable, durable, and of rather simple design.